This example shows the use of the Circle Profile in characterizing the sharpness or quality of an image with features that are radial in character. If the Circle Tool is centered properly, then an intensity profile along the circle will cross the feature edges roughly perpendicularly. Examination of this profile should yield measures of image quality or sharpness.
Here are sample steps using Lispix to examine the image of the retina of the human eye.
and adjusting the radius accordingly, or by using Profiles / Set Ring Radius / Times X / 2.5.
I moved the outer handle so that the radial line is horizontal. This is just to show where profile data starts - at this handle, going counter clockwise around the circle. Profile data always starts at this 3 O'Clock position, no matter the angular position of this handle.
Image intensities are multiplied by the scale factor you type in, and plotted radially, with zero being the circle.
The tool should then look like this:
- The blue pixels are those in the profiles.
- You can zoom the findus image and scroll it to see the same place. Note that the ring does not show the pixels in this way.
- The two images can be scrolled to exactly the same place using the Groups Tool. I just did it by eye here.
Here is Profiles / Save Profile as Text / Vals & Coords , after opening in Excel:
In my version of Excel, I opened Excel, used the Open menu changing the file type to "Text Files". The delimited button was the default - so I just clicked "Finish".
Lispix opens this text window, and prints the data into it. It can be copied and pasted directly into Excel:
where I have widened column A.
"Int Abs Dif" stands for Intensity - Absolute value of successive Differences. The first value should be the absolute value of the difference of intensities between the first and second pixel in the ring (starting at 3 O'Clock and going counter clockwise.) There is one fewer value in this profile than in the intensity profile. You can plot this profile using: Profiles / Profile Plots - Circular / Abs Diffs / Scale factor of 5.
or using Profiles / Profile Plots - Linear / Abs Diffs: